Scientific Advance: Human cloning for therapeutic use

May 16, 2013Carole No Comments »

The big news item yesterday was the announcement that Shoukhrat Mitalipov, a reproductive biology specialist at the Oregon Health and Science University and his colleagues produced embryonic stem cells from a human clone they produced. Their study, Human Embryonic Stem Cells Derived by Somatic Cell Nuclear Transfer, was published in Cell.

How they made a human clone:

1. Remove the nucleus (which contains  the DNA) from a human donated egg. The de-nucleated egg is now a sac filled with cytoplasm but no DNA. ( I expect there may be mitochondrial DNA from the egg donor but this is present as less than 1% of the DNA.)

2. Remove nucleus from another cell (in this case, a fibroblast type cell) obtained  from another person. Fibroblasts are a somatic cell type that gives rise to skin, for example.  For therapeutic cloning, the DNA for the clone comes from a patient who needs stem cell therapy. The clone that is produced is therefore a clone of the patient and has the patient’s DNA.

3. Transfer the DNA nucleus from the patient’s somatic cell (the fibroblast) to the  empty (no nucleus) donor egg using electrofusion, injection or other procedure.  The name for this procedure is Somatic Cell Nuclear Transfer, abbreviated SCNT in photo above.

4. The resulting embryo is cultured to the blastocyst stage. At this stage, in theory, it could be transferred to a human uterus to produce a human child, with DNA identical to the person who donated the fibroblast DNA.  That would be reproductive cloning.

5. For therapeutic cloning, the cloned embryo is dissected and the inner cell mass is removed, disaggregated and cultured further to produce stem cell lines (NT-ESC , Nuclear transfer – Embryonic stem cells) for all the cell types in the body. The cell type that needs repair (in the original donor) patient can be put to use to treat the patient. Because the new stem cells are made from the patient’s own DNA, tissue rejection is not an issue.

So what’s not to love with this approach? Patients get custom stem cells made for them to repair their hearts, their livers, or whatever organ is gone or going, and no human embryo produced in an IVF clinic (and otherwise meant to be a baby) was harmed.

But of course, it’s never that easy. Here are some of the concerns raised to date:

1. Slippery slope argument: Now that human cloning is technically feasible, it will be used for reproductive cloning, not just therapeutic cloning. First, reproductive cloning is illegal in most countries and most US states. Federal research dollars can’t be used to do reproductive cloning, so there are several barriers already in place to inhibit reproductive cloning. Some are calling for more restrictions. The other thing is that we don’t know how safe reproductive cloning is for the children produced. Since the early genetic imprinting is not through the normal pathways after fertilization, does this set the child up for health problems, possibly even cancer, down the road? There’s a lot we’d want to know first but whether anyone could ever legally (or ethically) do the research is questionable. The lead author of the paper, Masahito Tachibana, has stated that the next paper will explain why their approach will not work for reproductive cloning.

Some of the same concerns exist for therapeutic cloning. Can we be sure that the embryonic stem cells produced from a clone are normal enough not to give rise to health problems (even cancer) after they are injected into the patient?

2. Baby selling argument: Eggs are purchased from donors. We already pay donors for sperm and compensate egg donors for their time and trouble so it is not unprecedented. Also, eggs are not embryos and so egg selling. in my opinion,  is not akin to baby selling.

3. Pro-life argument: Any human embryo produced should only be used to make a baby (every embryo is sacred) and should not be destroyed/used for any other purpose. Human embryos should never be used as “parts” for therapy. The purpose or value of human embryos is what is at debate here. I can value human embryos and still believe it is okay to use them for an “alternative higher purpose” such as stem cell research or therapy. Others do not see this as an ethical option. The debate continues.

References and other articles about this scientific advance:

Cloning, Stem Cells Long Mired In Legislative Gridlock (NPR)

Cloning Is Used to Create Embryonic Stem Cells (New York Times) 

Patient-Specific Human Embryonic Stem Cells Created by Cloning (Scientific American)

Cloning FAQs page, National Genomic Research Institute

Original Paper: Human Embryonic Stem Cells Derived by Somatic Cell Nuclear Transfer (Cell)

© 2013, Carole. All rights reserved.

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